org.apache.zookeeper.common.AtomicFileOutputStream Maven / Gradle / Ivy
/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.zookeeper.common;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FilterOutputStream;
import java.io.IOException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/*
* This code is originally from HDFS, see the similarly named files there
* in case of bug fixing, history, etc...
*/
/**
* A FileOutputStream that has the property that it will only show up at its
* destination once it has been entirely written and flushed to disk. While
* being written, it will use a .tmp suffix.
*
* When the output stream is closed, it is flushed, fsynced, and will be moved
* into place, overwriting any file that already exists at that location.
*
* NOTE: on Windows platforms, it will not atomically replace the target
* file - instead the target file is deleted before this one is moved into
* place.
*/
public class AtomicFileOutputStream extends FilterOutputStream {
private static final String TMP_EXTENSION = ".tmp";
private final static Logger LOG = LoggerFactory
.getLogger(AtomicFileOutputStream.class);
private final File origFile;
private final File tmpFile;
public AtomicFileOutputStream(File f) throws FileNotFoundException {
// Code unfortunately must be duplicated below since we can't assign
// anything
// before calling super
super(new FileOutputStream(new File(f.getParentFile(), f.getName()
+ TMP_EXTENSION)));
origFile = f.getAbsoluteFile();
tmpFile = new File(f.getParentFile(), f.getName() + TMP_EXTENSION)
.getAbsoluteFile();
}
/**
* The default write method in FilterOutputStream does not call the write
* method of its underlying input stream with the same arguments. Instead
* it writes the data byte by byte, override it here to make it more
* efficient.
*/
@Override
public void write(byte b[], int off, int len) throws IOException {
out.write(b, off, len);
}
@Override
public void close() throws IOException {
boolean triedToClose = false, success = false;
try {
flush();
((FileOutputStream) out).getChannel().force(true);
triedToClose = true;
super.close();
success = true;
} finally {
if (success) {
boolean renamed = tmpFile.renameTo(origFile);
if (!renamed) {
// On windows, renameTo does not replace.
if (!origFile.delete() || !tmpFile.renameTo(origFile)) {
throw new IOException(
"Could not rename temporary file " + tmpFile
+ " to " + origFile);
}
}
} else {
if (!triedToClose) {
// If we failed when flushing, try to close it to not leak
// an FD
IOUtils.closeStream(out);
}
// close wasn't successful, try to delete the tmp file
if (!tmpFile.delete()) {
LOG.warn("Unable to delete tmp file " + tmpFile);
}
}
}
}
/**
* Close the atomic file, but do not "commit" the temporary file on top of
* the destination. This should be used if there is a failure in writing.
*/
public void abort() {
try {
super.close();
} catch (IOException ioe) {
LOG.warn("Unable to abort file " + tmpFile, ioe);
}
if (!tmpFile.delete()) {
LOG.warn("Unable to delete tmp file during abort " + tmpFile);
}
}
}